A general image sensor is called a surface radiation type image sensor and has a configuration in which, after an imaging element (photodiode) is formed on a substrate, a wiring layer is stacked, and a color filter and an on-chip lens are formed thereon. A general image sensor can be formed in this manner because the wiring layer may be formed after the imaging element is manufactured.
In a wiring layer formed on an upper layer of the imaging element, a hole is formed to enable light to be transmitted in a pixel unit so as not to disturb reception of the light in the pixel unit. For this reason, in the surface radiation type image sensor, the light is partially reflected or shielded by the wiring layer around the hole, the light may not be appropriately received, and a subject may not be imaged at an original brightness.
Therefore, a so-called back surface radiation type image sensor (or a back illuminated sensor) has been suggested; the back surface radiation type image sensor may have a structure in which, after the imaging element is manufactured, the wiring layer is stacked thereon, the substrate is reversed, the substrate of the back surface side is polished to a predetermined thickness, and light may be received from the back surface side. In the back surface radiation type image sensor, because the color filter and the on-chip lens are formed directly on the imaging element, the subject can be imaged at the original brightness without disturbing incidence of the light on the imaging element similar to the wiring layer in the surface radiation type image sensor.
Recently, imaging devices using the back surface radiation type image sensor have been utilized in a variety of applications; accordingly, various application technologies of the back surface radiation type image sensor have been developed (refer to Patent Literature 1).